MacOS Sierra - time machine stuck preparing backup on Network devices

I too had a similar problem to what you are describing.

This morning I swapped the router for an old Netgear one and it worked fine... but slowly (DG834G)

So I took a look at my TP-Link D9 router and checked to see if there was newer firmware for it. There was so I updated the router firmware and bingo, my TimeMachine back up now works via a wireless connection to the router again.

Thanks to you all for your patience

Thats prob just coincidence or u had an anomoly issue

On multiple macs now, all i had to do was move / copy the old backup out of the backup target TM location, and start a new backup. Sierra doesnt like the name or format of the old pre-Sierra backups so it gets confused or something

Or u can just delete the old backup but i wouldnt until u have a good recent backup stored somewhere else

Well this is what TP-Link Support said:

We have analysed the problem in the last few days, too. And We find that we didn't add the data transmit support for Apple's Time machine for some of our product. We will consider to complete that in the future.

I suspect that Apple changed something in the upgrade to Sierra.

Check your router firmware...

Steve

I followed this PR Reset process. Success! My Timecapsule now backs up correctly. Thank you.

Prior to pursuing the PR Reset, I spent four days patiently applying the Apple Support advice here, to no avail. Why doesn't the Apple Support article refer to the PR Reset process?

Thanks, this worked for me.

This worked for me. Thanks.

Thank you so much for the tip! I was trying to backup for a year. I thought there was something wrong with external device 😁